title: A generalized model to estimate the statistical power in mitochondrial disease studies involving 2×k tables.
abstract: BACKGROUND
  Mitochondrial DNA (mtDNA) variation (i.e. haplogroups) has been analyzed in regards to a number of multifactorial diseases. The statistical power of a case-control study determines the a priori probability to reject the null hypothesis of homogeneity between cases and controls.
  
  
  RESULTS
  We critically review previous approaches to the estimation of the statistical power based on the restricted scenario where the number of cases equals the number of controls, and propose a methodology that broadens procedures to more general situations. We developed statistical procedures that consider different disease scenarios, variable sample sizes in cases and controls, and variable number of haplogroups and effect sizes. The results indicate that the statistical power of a particular study can improve substantially by increasing the number of controls with respect to cases. In the opposite direction, the power decreases substantially when testing a growing number of haplogroups. We developed mitPower (http://bioinformatics.cesga.es/mitpower/), a web-based interface that implements the new statistical procedures and allows for the computation of the a priori statistical power in variable scenarios of case-control study designs, or e.g. the number of controls needed to reach fixed effect sizes.
  
  
  CONCLUSIONS
  The present study provides with statistical procedures for the computation of statistical power in common as well as complex case-control study designs involving 2×k tables, with special application (but not exclusive) to mtDNA studies. In order to reach a wide range of researchers, we also provide a friendly web-based tool--mitPower--that can be used in both retrospective and prospective case-control disease studies.
authors.affiliation: Unidade de Xenética, Departamento de Anatomía Patolóxica e Ciencias Forenses, and Instituto de Ciencias Forenses, Grupo de Medicina Xenómica (GMX), Facultade de Medicina, Universidade de Santiago de Compostela, Galicia, Spain.
authors.forename: Jacobo
authors.initials: J
authors.lastname: Pardo-Seco
authors.forename: Jorge
authors.initials: J
authors.lastname: Amigo
authors.forename: Wenceslao
authors.initials: W
authors.lastname: González-Manteiga
authors.forename: Antonio
authors.initials: A
authors.lastname: Salas
mesh_terms: D016022:Case-Control Studies; D004272:DNA, Mitochondrial / Q000235:genetics; D006801:Humans; D020407:Internet; D028361:Mitochondrial Diseases / Q000235:genetics / Q000503:physiopathology*; D008962:Models, Theoretical; D014584:User-Computer Interface
chemical_list: D004272:DNA, Mitochondrial